The present invention relates generally to a circuit board, a mounting structure, a mounting method, and an electronic apparatus, and more particularly to a circuit board that mounts an electronic device (for example, a condenser) that has bumps arranged two-dimensionally on its front surface or both of front and back surfaces or its mounting structure. The present invention is suitable for a printed circuit board on which a various electronic devices are mounted, for example, a motherboard or a graphic board, and for an electronic apparatus (for example, a server or a mobile phone) that contains the printed circuit board.
For recent widespreading of the electronic apparatus, the demand for the apparatus of higher performance and the cheaper is now growing. As a structure for mounting the electronic device such as a condenser on the printed circuit board used in the electronic apparatus such as a personal computer, a server, a mobile phone, or a PDA (personal digital assistants), FIG. 5 shows a connection of bumps 4 that are arranged two-dimensionally on an electronic device 2 and pads 8 that are arranged two-dimensionally on a circuit board 6. The bumps 4 and the pads 8 are connecting terminals and are generally formed approximately hemispheric with using solder. The bumps 4 and the pads 8 are arranged in 4×4 square arrangement respectively and are arranged V-lines (high voltage terminal lines) and G-lines (ground terminal lines) alternately.
As shown in FIG. 5A, the electronic device 2 is conventionally mounted on the circuit board 6 by the process of contacting the bumps 4 to the corresponding pads 8, putting the electronic device 2 and the circuit board 6 into a reflow furnace to heat them and melt solder, and connecting the bumps 4 with the pads 8. And as shown in FIG. 5B, the electronic device 2 is observed from the side by eye and “short/open check” that is an inspection for checking a gap of the circuit board 6 and the package of the electronic device 2 is approximately 0.1 mm evenly has been done. References 1 to 4 disclose the structures or the methods for mounting the electronic device onto the circuit board.
Reference 1: Japanese Patent Application Publication No. 11-274238
Reference 2: Japanese Patent Application Publication No. 2001-177226
Reference 3: Japanese Patent Application Publication No. 11-214442
Reference 4: Japanese Patent Application Publication No. 9-181208
However, an inspector has to be skillful because the inspection of the gap of 0.1 mm by eye is not easy. Therefore, the quality of the short/open check depends on the quality of the inspector and it is difficult to maintain a quality of the inspection constantly. And the short/open check needs a lot of time for observing by eye from several directions. So, a short/open check that is simple, high quality, and automatic is demanded to be real.
The electronic device 2 as is used generally has bumps 4 arranged squarely like shown as a conventional example. It may cause the mis-mounting of the electronic device 2 in a direction of 90° as shown in FIG. 5C. The mis-mounting cannot be found in the short/open check which uses eyes. The mis-mounting of the electronic device 2 will be finally found in a operation test of the circuit board 6 done after a lot of electronic devices were mounted on the circuit board 6.
In removing the electronic device 2 from the circuit board 6, there is no choice except using a pinching means such as tweezers or pliers (a removing with destruction method) as shown in FIG. 6A nor melting solder by blowing hot air from outside of the electronic device 2 (a hot air method) as shown in FIG. 6B. However, in the removing with destruction method, the electronic device 2 is destroyed with excessive stress and cannot be reused. The residue such as a part of the electronic device 2's bump 4 is left on the circuit board 6 after removing the electronic device 2, and should be taken off to reuse the circuit board 6. In the hot air method, it is easy to melt solder of the bumps 4 arranged near around the package 10 of the electronic device 2, and is difficult to conduct the heat to the solder of the bumps 4 arranged near the center of the electronic device 2. When removing the electronic device 2 in this state, the electronic device 2 should be taken off by using the pinching means and might be destroyed. Heating the bumps 4 sufficiently so as to melt solder of the bumps 4 arranged near the center of the electronic device 2 causes problem because of too much heat stress of the circuit board 6 and the electronic device 2.